-Then watch the beginning of video in France, and tell me, what are these conditions fot these 2 airplanes that would make their trails so different, considering they are flying mere 200 meters apart.
I don't even have to watch the video to answer this one. It's simple, airplanes in cruise flight simply
do not fly a mere 200 meters apart. That is much too close for safety.
The separation rules are complex and depend on type of air space, altitude, and direction of separation. Aircraft are allowed to come closest to each other in the vertical direction because airplanes have traditionally measured vertical position much more accurately than horizontal position. In most places, in cruise under 29,000 ft the closest they can
ever come is 1,000 ft vertically. Above 29,000 ft, that increases to 2,000 ft vertically. And of course atmospheric conditions for contrail formation can vary greatly over that 1,000-2000 ft. (Remember how the device that measures altitude actually works and why it's so accurate. That's just one atmospheric property that varies quickly with altitude.)
But the separations are likely even greater. Up to 29,000 ft the odd thousand ft levels are assigned to eastbound flights and even thousands to westbound flights, so two aircraft going the same way and in the same geographic location will necessarily be at least 2,000 ft apart vertically. Above 29,000 ft only the odd flight levels are used, increasing the minimum altitude difference between aircraft going in the same direction to 4,000 ft.
Minimum separations in the horizontal directions (ie, at the same altitudes where the air properties for contrail formation would be the same) depend on the altitude and kind of airspace. In radar controlled airspace, horizontal en-route separations are 5 to 10 nautical miles. When two aircraft are following the same route, they cannot come closer than 10 or 15 minutes flying time.
The rules are complex and under revision to permit more efficient use of the air space, but it is still obvious right off the bat that you aren't seeing two cruising aircraft a mere 200m apart. You are seeing them at different altitudes and/or in different locations where the atmospheric conditions for contrail formation can be very different.
You need not guess about the altitude of the aircraft you see. Real time flight tracking data is available online at several sites, e.g.,
http://www.flightaware.com. You can see for yourself just how far apart they are and determine for yourself the altitudes at which contrails are currently forming.
